Dielectric compositions



Patented Mar. 31, 1942 DIELECTRIC COMPOSITIONS Frank M. Clark,Pittsfield, Mass, assignor to General Electric Company, a corporation ofNew York No Drawing. Original application March 6, 1940,

Serial No. 322,599. Divided and this application November 8, 1940,Serial No. 364,864

8 Claims.

The present application is a division of my application Serial No.-322,599, filed. March 6, 1940.

The present invention comprises new compositions having a combination ofproperties which render such compositions especially suitable fordielectric and insulating purposes in electric apparatus, and, inparticular, as impregnants for electric capacitors.

In my priorUnited States Patent No. 2,019,337, patented October 29,1935, I have described and claimed compositions consisting essentiallyof nitrochlor or other nitro-halogen derivatives of polyphenylcompounds, The compositions described in this patent are prepared by thenitration of halogenated polyphenyl compounds.

Ortho nitrodiphenyl is a crystalline solid, melting at about 375 C. Itmay be prepared by treatment of diphenyl with a nitration mixture ofnitric and sulphuric acid at approximately 35 to 40 C. At 25 C. it hasadielectric constant of about 3. Even at room temperature the originalcapacity of such capacitors soon decreases to approximately 50 per centof the initial value. This unhalogenated material appears to be whollyunsuitable for use as a capacitor impregnant.

The subject matter of the present divisional application comprisescompositions including as one ingredient materials made by halogenatingnitropolyphenyl compounds, such for example as ortho nitrodiphenylcompounds, and including as a second ingredient this type of compound inthe unhalogenated state. Such compositions possess properties which arehighly advantageous for the dielectric field, for example, causingcapacitors impregnated therewith to have a substantially constantcapacity with rise of temperature or to exhibit increasing capacity withrise of temperature.

For example, the nitrochlordiphenyl composition described in my priorpatent has a dielectric constant of '7 or 8 at 100 C., 1000 cycles.

The new nitrotetrachlor diphenyl products described and claimed inparent application Serial No. 322,599 and constituting a part ofcompositions embodying my present invention have materially higherdielectric constants under the same conditions. Other physicalproperties of these new nitrochlor products as, for example, highelectrical resistivity also are highly advantageous, and particularly soin the high voltage The chlorination of ortho nitrodiphenyl may Table IPreponderant isomers formed Per cent chlorine introduced 'iemporature oichlorination, ccntigrade Mono. Di. Tri. Tetra. Penta. Hexa.

The chlorinated products are purified by washing with an aqueousalkaline solution and by distillation, as well understood. For example,the chlorinated mixture is washed with water to remove acid reactant andreaction products, and then is filtered to remove catalyst. Thereupon,it is washed with a l to 3 per cent sodium hydroxide aqueous solutionuntil neutral. The neutral product is repeatedly washed with water toremove all traces of alkali and then is carefully distilled. Adistillation under reduced pressure is preferred to avoid decompositionat high temperatures. A 20 millimeter pressure is convenient.

The following properties characterize the products listed in Table I:

Table I] Boning Density (tem- I Color Pour 1 mge erature as P. point,Condition at 25 0. cent (20 9 coslty m glven) A. cent.

Mono 200-217 1.305 (15) 2 4 35 Yellow liquid. Di 220-233 1. 400 (15) 2 744 Yellow liquid and crystals. 'lri 238-250 1. 470 (25) 2% 18 51 Yellowliquid. letra 250-260 1.490 (100) 2 31 73 Yellgw viscous liqin Dentin...200-270 1.555 (100) 1% 48 112 Yellow crystalline resin. Hem..." 270-2801.640 (100) 1% 725 Semi-crystalline resin.

N. P. A. is an abbreviation meaning Notional Petroleum Association.

"Viscosity values are given Saybolt Universal units taken at atemperature or For some purposes a material containing about e1 per centchlorine is preferred. This material consists largely of isomers of thetetrachlor ortho nitrodiphenyl although it may be associated with somecompounds of lower and some compounds of higher chlorine content. itselectrical resistivity is high, at 25 C. being 16,600X ohms percentimeter cube. its dielectric constant at 25 C. is 19.0.

Thechiorinated composition containing about 34: per cent chlorine andconsisting iargely of the trichlor ortho nitrcdlphenyl has advantagesover the tetrachlor product for some purposes. The electricalresistivity of this composition at 25 C. is 022x10 ohms. The dielectricconstant at 25 C. is 22 and at 50 C. is 19.9.;

The resistivity of the new chlorination prodpacity and othercharacteristics of a comparison capacitor unit. A. comparison capacitorof assumed fixed dimensions which contains spacers of lsraft paper, whenimpregnated with pentachior diphenyl has a capacity of 3 microfarads.When such comparison capacitor is impregnated with ortho nitrotetrachlor diphenyl alone (that is, unassociated with a modifyingingredient), it has at 25 C. a capacity of 4.40 microfarads and a powerfactor of .50 per cent.

In accordance with my present invention, the chlorinated orthonitrodiphenyl'products are associated with a modifying material wherebycompositions having various new and unpredictable characteristicsare'found to be obtained.

As such modifying materlals, 1 may employ various nitratedarylpolynuclear hydrocarbons, one example being dlnitrodiphenvl (unhalogen-=ated) This material in a preferred form is substantially the 2,4dinitrodiphenyl, but may contain substantial amounts of other isomers,as for example, the 2,2 dinitrodiphenyl. The preferred product is ayellow solid having a melting point of about 75110 80 0. Its resistivityat'25" C. is

4270 10" ohms per c111 Awide range of proportions may be employed, thefollowing being given as illustrative examples of mixtures of dielectriccompositions, although it should be understood that my invention is notto be limited in scope to the described compositions.

EXAMPLE '1 A mixture consisting by weight of 75 per cent (or 3 parts)ortho nitro tetrachlor diphenyl and 25 per cent (or 1 part) ofdinitrodiphenyl has a dielectric constant at 25 C. of 30, whichprogressively decreases as the temperature is aised, but

still being relatively high, namely, 2 .8 at100 C. When the abovecomparison capacitor is treated with this mixture it has at 25 C. acapacity of 4.83 microfarads. This capacity remains substantiallyunchanged as the temperature increases to about 100 C. The power factorof a capacitor unit impregnated with such a mixture in which the orthonitro tetrachlor diphenyl is a major ingredient at 25 C. is .46 percent, at

50 C. is .76 per cent, at 75 C. is 1.35 per cent, and at 100 C. is 1.30per cent.

EXAMPLE 2 .A mixture consisting of equal parts 01 dinitrodiphenyl andortho nitro tetrachlor diphenyl has Table Hi 25 C---" .45 50 C -u 1.0575 C 1.50 100 C 1.42

Exam ne 3 Mixtures consisting by weight of 25 parts of ortho nitrotetrachlor and 75 parts of dinitro diphenyl show the followingdielectric characterlstics:

Table I V Dielec- Temperature, centigradc tric constant The resistivityof this mixture atv 100 C. is 384x10 ohms per cm The following capacitorand power factor values characterize the same comparison capacitor unitimpregnated with this mixture:

Table V Capacity Percent Temperature, centlgrade lnmicropower I factorFor some purposes it. is advisable. to mix or blend the ortho nitrochlordiphenyl compositions with alpha nltronaphthalene (unchlorinatem EXAMPLE4' Table VI 'Capacity Per cent Temperature, centigrade in micro powerfarads factor It will be observed that the capacity rises with anincrease of temperature from 25 to 50 C., the power factor beingrelatively low and little subject to change. I

EXAMPLE 5 The comparison capacitor units when impreg nated with amixture of equal parts of these two ingredients have the followingcharacteristics:

Table VII Capacity Per cent Temperature, centigrade in micropower iaradsfactor EXAMPLE 6 When it is desired that capacitors containing orthonitrochlor diphenyl should have capacities which are substantiallyconstant over a wide range of temperatures, three parts of thenitrochlor product are associated with one part of alphanitronaphthaleneto produce an impregnant giving capacitors a high efllciency whichvaries very little with temperature change. The comiparison capacitorsin this case have the following characteristics:

Table VIII Per cent power factor Capacity in micro- Tempcrature,centigradc farads The various examples given herein are to be understoodas illustrative, and not as defining the limits of my invention. Similaradvantages are obtained over a wider range of-proportions thanrepresented by these examples. The nitro compounds to which I havereferred are illustrative of the class of polynuclear a'ryl compounds,but I do not wish to be limited thereto. Other nitrated polynuclearcompounds may be used in lieu of those above-mentioned, for example,nitro compounds of diphenyl methane, diphenyl ethane (dibenzyl),diphenyl ketone "and substitution products of those mentioned as, forexample, nitrodiphenyl benzene.

What I claim as new and desire to secure by, Letters Patent of theUnited States is:

1. A material consisting of a mixture of a substantial proportion ofchlorinated ortho nitrodiphenyl and a substantial proportion of nitratedaryl polynu'clear hydrocarbon.

2. A material consisting of a mixture of a substantial proportion of achlorination product of nitrodiphenyl and 'a substantial proportion ofdinitrodiphenyl.

3. A material consisting of a mixture of a substantial proportion of aclhorination product of K nitrodiphenyl and a substantial proportion ofalphanitronaphthalene.

4. A material consisting of a mixture of a substantial proportion of achlorination product of ortho nitrodiphenyl and a substantial proportionof ortho nitrodiphenyl.

5. A composition comprising substantial proportions of a chlorinationproduct of ortho nitrodiphenyl containing about 34 to 41 per cent.chlorine and a substantial proportion of unhalo- FRANK M. CLARK.

